Fifty years ago this month, the Catholic Church embarked on a period of soul-searching that reverberated far beyond St. Peter's Basilica in Rome. Pope John XXIII called Catholic bishops across the globe to the Second Vatican Council, opening the windows of a monarchical church to the modern world.

The first Catholic president, John F. Kennedy, sat in the White House. Clergy infused the civil rights movement with moral transcendence. These were heady days for religious progressives.

They were also fleeting. Just two decades later, Jerry Falwell made the religious right the public face of Christianity. Today, at a time when debates over the role of faith in politics are as prickly as ever, Catholic nuns in the United States are reawakening the spirit of Vatican II and inspiring a new generation of disillusioned Christians as they face harsh rebuke from an increasingly conservative hierarchy.

Vatican II met for three years beginning in 1962 and stirred groundbreaking changes: building ecumenical bridges, especially in Christian-Jewish relations; permitting Mass to be celebrated in local languages instead of only in Latin; and expansively defining the church as "the people of God." The council was guided by what John XXIII called aggiornamento, or "updating" - a profound change given the church's previous rejection of modernity and liberalism as heresies.

The American Jesuit priest and theologian John Courtney Murray, who a decade earlier had faced Vatican censure for his writings on conscience and religious freedom, became a leading intellectual light of the council. Nuns, encouraged by the council's reformist instincts, emerged from convents to "live the Gospel" in blighted communities. These women continue to serve in prisons, hospitals and war-torn countries. Many took on leadership positions that belie antiquated stereotypes.

In the years after the council, however, the church retrenched.

The next pope, Paul VI, ignored the majority report of his own theological commission when in 1968 he declared birth control to be an "intrinsic evil" even for married couples. The charismatic Pope John Paul II (1978-2005) cracked down on "liberation theology" movements in Latin America led by priests and nuns standing with the poor in the face of oppressive right-wing governments. He also offered stinging critiques of unfettered capitalism and made historic steps to improve Christian-Jewish relations. But his 27-year year papacy was largely defined by a conservative sexual theology, a staunch defense of the all-male priesthood and blindness to the clergy sexual abuse crisis that engulfed the church.

Now Pope Benedict XVI's doctrine office has cracked down on an organization called the Leadership Conference of Women Religious, which represents most U.S nuns. A scathing report from the Vatican in April blasted the group for "promoting radical feminist themes incompatible with the Catholic faith." It chided the nuns for largely focusing on social justice at the expense of speaking out against same-sex marriage and abortion. The Vatican appointed Seattle Archbishop J. Peter Sartain to oversee the conference.

The Vatican's tone-deaf scolding of self-sacrificing nuns is just the latest sign that church leaders may be dragging Catholicism, known for social justice and intellectual rigor, into the reactionary arms of fundamentalist Christianity. On the same day the Vatican sought to rein in American nuns, it reached out to reconcile with the Society of St. Pius X, a traditionalist group founded by the late French Archbishop Marcel Lefebvre that broke with the church in the wake of Vatican II.

And yet, puritanical Catholicism that fixates on policing sexual morality and claims to be the victim of a godless secular culture is unlikely to help the church flourish. Nearly 10 percent of U.S. adults are former Catholics, which makes them the third-largest U.S. "denomination."

Even some bishops are sounding the alarm. Cardinal Carlo Martini of Milan, in a final interview before his death this summer, lamented that the church is "200 years out of date" and so focused on lecturing about sexuality that its leaders are in danger of being perceived as a "caricature in the media."

U.S. Catholics bishops make wonderful statements about the importance of unions, comprehensive immigration reform and the need to protect social safety nets now threatened by anti-government ideologues. In letters to Congress, they have described a budget proposal by Rep. Paul Ryan, R-Wis., a Catholic now vying for the vice presidency, as failing "a basic moral test."

But compared to the church's frequent public denunciations of "pro-choice" Democrats or its two-week Fortnight for Freedom campaign - launched with special Masses across the country in response to the Obama administration's contraception coverage requirements under healthcare reform - the bishops have put little institutional muscle behind challenging a GOP economic agenda that is anathema to Catholic social teaching.

Even the U.S. bishops' respected anti-poverty agency has been pressured by conservative Catholic activists to put ideology before care for the poor. A small nonprofit group in rural Colorado that helps Latino immigrants with healthcare and other basic needs lost more than half its funding from the Catholic Church because the group has an association with a statewide coalition that also happens to support gay rights.

Meanwhile, in a flashback to the McCarthy era, the Diocese of Arlington, Va., has required Sunday school teachers to swear loyalty oaths.

In the face of this embattled, defensive Catholicism, it's no wonder that many Catholics have been cheering as a Nuns on the Bus tour rolled through several states this summer and into the fall. The trip highlighted the inspiring work sisters do in leading service agencies that feed the hungry and care for the sick.

"Preach the Gospel always and when necessary use words," St. Francis of Assisi instructed. These nuns live that admonition every day. By challenging members of Congress who voted for Ryan's draconian budget (which slashes nutrition programs for low-income women and infants), and by supporting the Affordable Care Act, the nuns also showed that being "pro-life" doesn't stop with defending life in the womb.

Five decades removed from the aura of hope that animated Vatican II, the Catholic Church stands at a crossroads. Do the Vatican and U.S. bishops really want a smaller, "purer" church, where the door is slammed in the faces of nuns, theologians and progressive Catholics? Catholicism has few better ambassadors than the nuns on the bus. Our church marginalizes them at its own peril.

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John Gehring is Catholic program director at Faith in Public Life, an advocacy group in Washington, and a former assistant director for media relations at the U.S. Conference of Catholic Bishops. He wrote this for the Los Angeles Times. Distributed by MCT Information Services.